1. Field of the Invention
This invention relates to a composite material for sliding surface bearings, in which a polymeric matrix is bonded to a metallic rough base surface to form a friction contact or sliding layer in a thickness from 0.01 to 2.0 mm over the peaks of the rough base surface.
2. Background Information
The use of polymers in the manufacture of sliding surface bearings in which the sliding surfaces are defined by walls consisting of a single material is restricted because polymers have a relatively low strength, a large thermal expansion and a low thermal conductivity. It has been attempted to avoid such restriction in that a polymeric matrix containing optional additives, such as lead, molybdenum disulfide, graphite, glass fibers or other inorganic fibers, individually or in combination, is rolled or pressed onto a rough base surface consisting of woven metal mesh or expanded metal, and is subsequently sintered (East German Patent Specification No. 30,963, German Patent Specification No. 2,001,101, European Patent Specification No. 40,448).
In accordance with German Patent Specification No. 2,928,081 the fluorine-containing polymer which constitutes the matrix is rolled or pressed directly on a rough base surface which has been formed by a mechanical or chemical roughening of the surface of a metallic backing layer, which preferably consists of steel, or on a rough base surface formed by a sintered or sprayed-on porous layer which has been provided on the metallic backing layer in a thickness from 0.2 to 0.6 mm and consists of a metallic material having good friction or sliding properties, whereafter the polymer is applied to the rough base surface in such a manner that a friction contact or sliding layer in a thickness from 30 to 500 .mu.m over the peaks of the rough base surface is provided. The rough base surface ensures an excellent bond between the matrix and the backing layer so that the sliding surface bearing elements made from the composite material for sliding surface bearings are very similar with regard to interference fit, elastic properties and thermal expansion to metallic materials for sliding surface bearings and for this reason can also be used in relatively small wall thicknesses.
In comparison with sliding surface bearings in which the sliding surfaces are defined by walls consisting of a single polymeric material, bearing elements made of composite materials for sliding surface bearings afford the advantage that they have a higher thermal conductivity and a higher strength. Besides, the sliding surface bearing elements made of the composite material for sliding surface bearings usually have a very high load-carrying capacity up to about 150 N/mm.sup.2, although this is achieved only at extremely low sliding velocities of up to 1 m/sec. A true limit in the case of oil-less operation is believed to be at 2 meters per second and it will be understood that an appreciable load cannot be tolerated at such a sliding velocity. For this reason, such composite materials for sliding surface bearings have been used mainly for sliding surface bearing elements which are subjected to oscillating motions, such as hinge bearings. But sliding surface bearing elements made of composite materials for sliding surface bearings are also widely used as guide bushings in shock absorbers for motor vehicles.
Materials for sliding surface bearings as described in European Patent Specification 40,448 can be cut and punched out as desired and such materials ensure that no portions of the expanded metal will be detached as the material is punched or cut out during its subsequent processing or use. Besides, material for sliding surface bearings has a comparatively high dimensional stability so that it can easily be automatically inserted into bearing bushings and split bearing shells during assembling operations. When the friction contact or sliding layer provided on the lands of the expanded metal has been worn off, the expanded metal itself will have very good emergency running properties.
Maintenance-free material for sliding surface bearings is inserted mainly into bearing bushings and split bearing shells in which a hydrodynamic lubrication is not provided, so that a progressive wear must be expected in spite of the presence of substances which influence the frictional and sliding properties, such as lead and glass fibers. Besides, the use of lead in the friction contact or sliding layer imposes a limit on the field of application of the materials for sliding surface bearings, because such materials cannot be used in certain machines, particularly in machines used in the pharmaceutic and food-processing industries.